This invention relates in general to the manufacture of slip joints, such as are commonly used in vehicle drive train systems, for transmitting rotational force or torque between telescoping members, while accommodating relative axial movement therebetween. In particular, this invention relates to an improved method for manufacturing a splined member, such as a male or female splined shaft, having a low friction coating applied thereto for use in such a slip joint.
In most land vehicles in use today, a drive train system is provided for transmitting rotational power from an engine/transmission assembly to an axle assembly so as to rotatably drive one or more wheels of the vehicle. A typical drive train system includes a driveshaft assembly that is connected between an output shaft of the engine/transmission assembly and an input shaft of the axle assembly. To accomplish this, a first universal joint is connected between the output shaft of the engine/transmission assembly and a first end of the driveshaft assembly, and a second universal joint is connected between a second end of the driveshaft assembly and the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft assembly to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes thereof.
Not only must the drive train assembly accommodate a limited amount of angular misalignment between the engine/transmission assembly and the axle assembly, but it must also typically accommodate a limited amount of relative axial movement. A small amount of such relative axial movement frequently occurs when the vehicle is operated. To address this, it is known to provide one or more slip joints in the driveshaft assembly of the drive train system. A typical slip joint includes male and female telescoping members having respective pluralities of splines formed thereon. The male splined member has a plurality of outwardly extending splines formed on the outer surface thereof yhat cooperate with a plurality of inwardly extending splines formed on the inner surface of the female splined member. Thecooperating splines of the male and female members provide a rotational drivingconnection through the slip joint, while permitting a limited amount of relative axial movement therebetween. The slip joint may be provided at the ends of the driveshaft assembly or in the interior thereof.
In the past, the splined members have been formed by a machining process, wherein material was removed from the member to form the splines. To accomplish this, the member was initially formed having a surface of predetermined size and shape. Then, a cutting tool (typically a hobbing tool) was moved into engagement with the surface of the member to form the splines by removing material therefrom. The remaining material on the member formed the plurality of splines. As a result of this machining process, the splines were formed having relatively square faces, i.e., faces that were generally flat and extended generally radially relative to the rotational axis of the member. Then, the splined member was coated with a material having a relatively low coefficient of friction. The low friction coating was provided to minimize the amount of force required to effect relative movement between the two splined members. Also, the low friction coating provided a relatively tight fit between the cooperating splines of the two splined members, thus minimizing any undesirable looseness therebetween while continuing to allow free axial movement.
Although the above-described machining process for forming the splines has functioned satisfactorily for many years, it has been found to be somewhat inefficient. This is because the machining process has been found to be relatively slow and expensive to perform. Also, the machining process results in a quantity of scrap material that must be disposed of, which further complicates the manufacturing process. Thus, it would be desirable to provide an improved method for manufacturing a splined member, such as a male or female splined shaft, having a low friction coating applied thereto for use in a slip joint.
This invention relates to an improved method for manufacturing a splined member, such as a male or female splined shaft, having a low friction coating applied thereto for use in a slip joint. Initially, a length of cylindrical stock is provided having a predetermined outer diameter. The end of the cylindrical stock is then machined by any conventional process to form a preform including an end portion and a neck portion. Next, the end portion of the preform is subjected to a cold working process by a conventional roll forming machine or similar tool to form a plurality of splines about the circumference thereof. The cold working process is effective to re-shape the end portion of the preform to form the splines without the removal of any material therefrom. As a result, each of the splines is formed having a generally involute cross sectional shape, wherein opposed sides of the splines are relatively gently curved between the inner roots and the outer ends thereof. The splines define a major diameter that is somewhat larger than the initial outer diameter of the preform and a minor diameter that is somewhat smaller than the initial outer diameter of the preform. Thereafter, the splines and the neck portion of the preform are coated with a conventional low friction material to form the splined tube shaft. A broaching machine or similar apparatus is used to precisely shape the solidified low friction material about the splines.